Hume claims that judgments of causality are completely constructed by the mind and they are a result of "habit" or "custom." We have a habit of thinking causally. But Hume does not say this is a bad thing, since without this habit we would not be able to function in everyday life. He even calls causality the "cement of the universe."
For Hume, our judgments of causality are determined by three factors: 1) constant conjunction: we continuously see one event that follows from another event in experience. For example, I see that one ball hits another ball, and that second ball moves, and this has happened many times; 2) contiguity: the two things must be close to each other in space and time; and 3) association between ideas: I have an idea of one ball moving, and the idea of another being hit and moving.
So, causality does not belong in the objects seen, but only in the mind. Causality is not a real feature of the world, but only a way we interpret events in the world. In this way, Hume's account of causality points to his broader position that we cannot have any knowledge of the world---or even be in a position to know that we have knowledge.

Hume observes that while we may perceive two events that seem to occur in conjunction, there is no way for us to know the nature of their connection. Based on this observation, Hume argues against the very concept of causation, or cause and effect. We often assume that one thing causes another, but it is just as possible that one thing does not cause the other. Hume claims that causation is a habit of association, a belief that is unfounded and meaningless. Still, he notes that when we repeatedly observe one event following another, our assumption that we are witnessing cause and effect seems logical to us. Hume holds that we have an instinctive belief in causality, rooted in our own biological habits, and that we can